The phrase "main block" typically refers to the central or primary section of something. It is the most important part or the core element. Full definition
The site features three main blocks with all the information about the author. (templatemonster.com)
In each period, or main block of time, $ 10,000 is put to work right before a large market correction, then given time (25, 17, 15, 8 and 5 years) then re-run for each block of time (25, 17, 15, 8 and 5 yrs.) (clark.com)